The aerodynamic resistance of commercial vehicles may be reduced using devices which include tarpaulins having an air intake in the rear area (see, for example, DE-OS 31 15 742 and U.S. Pat. No. 2,737,411). Such tarpaulins consist of basically airtight material and can be inflated by the dynamic pressure which develops during driving of the commercial vehicle. These tarpaulins are attached to the side edges of the vehicle's rear part and can be substantially tightened against the stationary vehicle (i.e., in the uninflated state) by interior restoring springs or backhaul cables. The drawback of such air-inflatable tarpaulins is the fact, that an aerodynamically optimal effective exterior contour cannot practically be produced since the flexible air-inflatable tarpaulin following the action of the inside and outside pressure, inflates to a shape that cannot exactly be determined. Also, the tarpaulin is relatively heavy and unwieldy and aesthetically unsightly in its folded state of rest.
Designs are also known (see U.S. Pat. No. 4,142,755) in which, on the rear part of a commercial vehicle, dimensionally stable frame parts and molded parts are used to counteract the problem of the fluctuating air conduction by the inflated air tarpaulin. Such designs are extremely expensive, and moreover, lengthen the vehicle structure. Also, it is possible only with high expenditure of labor to load or unload a commercial vehicle with such devices from the back side. As such, these conventional devices are not acceptable.
With this background, an object of the present invention is configuring a device with structurally simple means so that a profile favoring the path of air flow can be provided during travel without using aggregates of the vehicle in the vehicle's rear area and which is dimensionally stable in itself so as to constantly reduce the aerodynamic resistance of the vehicle. In the state of rest of the vehicle, the rear area is to be basically unaffected, i.e., the loading possibilities are not to be impaired and the structure is to be optimized with respect to weight. Furthermore, it is especially required that with surface mountings for tarpaulins, the rear tarpaulin can be folded upward in a normal way to unload the vehicle.
The device of this invention achieves the above-stated object by means of a rear tarpaulin which serves as a component of an inflatable air bladder leaving rigid spoiler elements (e.g., rigid polyurethane foam or similar light-weight materials). The device of the present invention is thus dimensionally stable since the spoiler elements are spreadable, i.e. angularly adjustable, by integration in the tarpaulin material of the air bladder or by direct attachment thereto, depending on the extent of the inflation of the air bladder. Thus, an optimal path of air flow is achieved in the area behind the contour edges at the rear of the vehicle, by virtue the dimensionally stable spoiler elements, it is assured that the overall profile at the rear of the vehicle during driving undergoes no shape changes whatsoever which could adversely affect the path of air flow. In the state of rest of the vehicle, i.e., with uninflated air bladder, the parts being used for shaping occupy only minimal space. In this regard, the spoiler elements as a component of the rear tarpaulin extend parallel to the rear of the vehicle and contribute only to a very slight increase of the total vehicle length. The rear tarpaulin forming the air bladder and carrying the spoiler elements is able to be handles normally with only slightly increased weight when the vehicle is loaded or unloaded on the back side. In this case, the rear tarpaulin can be folded upward as is conventional. The spoiler elements despite their dimensional stability are no obstacle to this type of handling of the rear tarpaulin since they are segmented.
The device for reducing the aerodynamic resistance according to this invention can also be used in an especially advantageous way in the gap between a truck tractor and a trailer for attaching to the rear part of the truck tractor since the spoiler elements may be provided with length-adjustable cables. The spoiler elements are thus adjustable in any angular position and provide for an optimal path air flow to be achieved in the gap between the truck tractor and trailer vehicle.
The idea inherent in the invention of the angular positioning of dimensionally stable spoiler elements by an inflatable air bladder can also be used in commercial vehicles with solid surface mountings. For example, the rear doors of a commercial vehicle can each be provided with an air bladder carrying spoiler elements and a separate air intake per air bladder is provided on the top side of the vehicle or on its side.
Advantageous embodiments and further aspects of this invention will be described in greater detail below.